Fix: Change secondary button focus style in dark mode

[dsmchen]

Because

Currently, focus style colour contrast ratio is approx 2:1. It should be at least 3:1.

This PR

• Change secondary button focus style in dark mode.

Issue

Closes #5202

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the keyword: brief description of change format, using one of the following keywords:
  • Feature - adds new or amends existing user-facing behavior
  • Chore - changes that have no user-facing value, refactors, dependency bumps, etc
  • Fix - bug fixes
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• I have verified all tests and linters pass after making these changes.
• If this PR addresses an open issue, it is linked in the Issue section
• If applicable, this PR includes new or updated automated tests

[KevinMulhern]

LGTM, thanks @dsmchen